The diffusion of sterically hindered amines with molecular weight 1364, 1393, 2286, and 2758 was studied in polypropylene between 60 and 130 degrees C. The diffusion coefficient changes with time and plots log D vs 1/T are given as broken lines for additives with molecular weight 2286 and 2758. IR data show that changes in the polymer structure during diffusion occurs. Slow diffusion of the additives in PP at elevated temperatures and high activation energies indicate that no migration at room temperature should take place.